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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 6 |
| 4 | 24 |
| 5 | 70 |
| 6 | 900 |
| 7 | 10514 |
| 8 | 88368 |
| 9 | 969966 |
| 10 | 14565660 |
| 11 | 210128842 |
| 12 | 3101829192 |
| 13 | 53657039462 |
| 14 | 1011396628788 |
| 15 | 19614301352130 |
| 16 | 407298714601056 |
| 17 | 9155878501901278 |
| 18 | 216531181241189964 |
| 19 | 5365383438167708858 |
| 20 | 140625865483389408120 |
| 21 | 3879395530456330528854 |
[1,0,0,6,24,70,900,10514,88368,969966,14565660, 210128842,3101829192,53657039462,1011396628788, 19614301352130,407298714601056,9155878501901278, 216531181241189964,5365383438167708858, 140625865483389408120,3879395530456330528854] |